Presensitized patients pose a large clinical problem in renal transplantation today. They are increasing in numbers and their accelerated and vigorous immune responses lead to very poor subsequent transplant survival rates. Clinical and animal data strongly suggest that the balance of immunoregulatory mechanisms ("help" vs. "suppression") dictates ultimate success or failure of any graft. It is apparent from such data that primary immune responses such as those seen in a patient receiving a first graft differ significantly from the secondary type of responses seen in the presensitized patient. The specific aim of this proposal is to use the in vitro secondary cell mediated lympholysis test and the antibody secretion plaque assays as models for the human T cell and B cell anamnestic responses. We will investigate the immunoregulation of such memory responses and also devise means to manipulate such processes to reduce the secondary effector phase of the immune response. Regulators of such memory cells will be identified by depleting OKT4+, OKT8+, Ia+ cells or monocytes from primed populations and testing either their intrinsic ability to respond to restimulation or to function as regulators in a 3 cell co-culture system also employing primed cells as the targets of regulators. Monoclonal antibodies will also be developed to specifically identify both secondary effector and regulator cells. Further, attempts will be made to preferentially induce suppression by altering the dose of antigen and/or the class or configuration of MHC antigen presented. This will be accomplished by using heat treated cells to present modified Class II MHC antigen plus Class I antigen and platelets and T cells as models for the presentation of Class I antigen alone. In addition, the lymphocytes of patients who have previously rejected a kidney graft (memory cells formed in vivo) will be restimulated in vitro to determine toward what class of alloantigen the memory cells are directed. Finally, the feasibility of down regulating such memory cells through the manipulation of antigen dose or type of stimulating cells will be tested. It is anticipated that succesful down regulation of memory responses in this in vitro model will suggest new, clinically feasible biologic approaches that will allow more successful retransplantation of the sensitized patient.